The goal of this project is to study the biomechanical characteristics of knees which have undergone reconstructions of the posterior cruciate ligament (PCL). A unique experimental technique developed in our laboratory will be used to directly measure resultant force in the PCL as fresh cadaveric knee specimens are subjected to controlled loading tests. The PCL will be excised and bone-patellar tendon-bone graft reconstructions will be performed. Knee laxity and graft forces after reconstruction will be compared to intact knee levels. The results will provide important information to the surgeon in terms of selecting a reconstruction technique, graft configurations, and graft pretensioning protocols. Tests with simulated muscle forces will help to formulate guidelines for rehabilitation activities for patients undergoing PCL graft reconstruction. Specific Aim 1: We will study the effects of single bundle and double bundle PCL graft configurations upon AP limits of motion (AP laxity) and graft forces during a series of tibial loading tests without (and in certain instances with) simulated muscle forces. Two reconstruction techniques (tibial tunnel and tibial inlay) will be studied using bone-patellar tendon-bone (BTB) grafts. The native PCL will be instrumented with a femoral load cell to establish baseline cruciate force levels during tibial loading tests and AP laxity will be measured at selected knee flexion angles. Tests will be repeated after PCL graft reconstructions have been performed using specific pretensioning protocols. Only an isolated PCL deficiency will be simulated; no associated collateral injuries will be created. Specific Aim 2: We will study the biomechanical effects of section (and subsequent reconstruction) of the posterolateral structures (LCL + popliteus tendon) in knees, which have undergone single bundle and double bundle PCL graft reconstructions using BTB grafts. The tibial inlay technique of PCL reconstruction will be used for these experiments. AP limits of motion and graft forces during tibial loading tests without (and in certain instances with) simulated muscle forces will be measured before and after section of the posterolateral structures, and compared to values recorded with the intact knee. Testing will be repeated after two different reconstruction procedures for the posterolateral structures have been performed: a BTB reconstruction for the LCL alone, and a modified two-tailed reconstruction using a semitendinosis tendon (which is designed to reconstruct both the LCL and popliteus tendon).